This invention relates to the maintenance of furnace boiler water walls and, in particular, to a method and apparatus for the repair of boiler tubes in water walls.
Furnace boiler water walls are used in commercial power plants, and are typically comprised of a plurality of boiler tubes joined by web sections. As is well known, leaks eventually develop in the tubes which require repair. It is desirable to cut out the leaking, damaged sections of the tubes and replace these sections completely from outside of the boiler furnace. By eliminating the need to enter the boiler to weld sections of replacement tube in place, personnel safety is improved and boiler down time is decreased.
In prior art repair methods, once the damaged tube section and adjacent web material is cut out, welding of a section of replacement tube from outside the boiler furnace is typically accomplished through windows cut in both ends of the section of replacement tube and existing tube ends. Internal welding of the section of replacement tube to existing tubing is accomplished through these windows. Patches or covers are then welded in place to close the windows and the web section is repaired.
Vucic, U.S. Pat. No. 4,047,659 is directed to a method of repairing water carrying tubes in a gas hood for a steel, furnace. Vucic discloses tack welding a section of replacement tube in place and thereafter cutting circular windows in the assembly by means of a circular cutter. Each window is cut at the point of connection between the existing tube and section of replacement tube. Internal welding of the section of replacement tube to the existing tube is then accomplished through the windows as before, and circular covers are welded into place and the web repaired.
Vucic's method was an improvement over the prior practice of hand cutting individual square or round windows and covers. Several drawbacks in this method, however, leave further improvement desirable. The small size of the hole which results restricts access to the interior of the tubes needed to make internal welds. Further to prepare the hole for welding the cover, the edges of the circular hole must be ground by hand. As well, additional web material must be cut away to use the hole cutter according to the method disclosed by Vucic.
Thus, while the prior art methods permit repair of leaking or damaged water wall tubes from one side, for example, outside a boiler furnace improvements in technique are needed and desired to decrease furnace down time and eliminate problems with existing methods.